This dog will not stop

I dont know what to do. My grandma has one of those white crusty dogs. This dog cannot walk properly, CONSTANTLY whines, slips on the floor when it does try to walk, can barley get up to eat, cannot clean itself so its back side is yellow, its face is disgusting and turning brown. The dogs front paws are different lengths because of how messed up its joints and bones are. and the dog wont let you touch it or pick it up because its in so much pain. I feel terrible for the dog, and terrible for what im about to say..but should this dog still be alive? This dog is 15 years old and cannot care for itself and will only let one person touch it (that person isn't me). The dogs favorite person is my uncle who is currently out of town on a business trip, which is why im here at my grandma's helping. between my 85 year old grandma, and the dog..im barley holding it together.

back to my point, this dog is falling apart and is held together with puppy pads, wet food, and a variety of medicine. It whines none stop and will just stare at you for hours. No matter what you do it wont stop. I feel like its way too late to start trying to correct any behaviors, especially with me being an 'outsider'.

Is it wrong keeping this dog alive? Is there anything to do to make this constant whining stop? I can't take it anymore.

**EDIT: This dog regularly goes to the vet, that's how its prescribed the medications it has. Theres not much the vet can do besides keep it comfortable if my grandma and uncle wont let it go.